Mobile wireless communication system and method of carrying out handover in the system

ABSTRACT

When a strength of an electric field for receiving wireless in downlink is equal to or smaller than a predetermined strength, the mobile communication terminal device  105  transmits a retrieval request to the retrieval server  102  through the first wireless station  103  to cause the retrieval server to start selecting a new wireless station, changes at least one of profiles (UTP) for transmitting wireless in uplink, and notifies the first wireless station  103  of the changed profile(s). The first wireless station 103 changes a profile or profiles (URP) for receiving wireless in uplink, corresponding to the changed profile(s) (UTP) for transmitting wireless in uplink, received from the mobile wireless terminal device, changes at least one of profiles (DTP) for transmitting wireless in downlink, and notifies the mobile wireless terminal device of the changed profile(s) (DTP) for transmitting wireless in downlink.

REFERENCE TO RELATED APPLICATION

This is a continuation application of U.S. patent application Ser. No.12/300,147 filed Nov. 10, 2008 and claims the benefit of its priority.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to handover technique in a mobile wirelesscommunication network. In particular, the invention relates to a mobilewireless communication system, a method of carrying out handover in thesystem, a wireless station used in the system, a mobile communicationterminal device used in the system, a program for causing the wirelessstation to carry out the method, and a program for causing the mobilecommunication terminal device to carry out the method.

2. Description of the Related Art

Many attempts have been made with respect to handover between adjacentwireless stations.

For instance, one of examples is disclosed in Japanese PatentApplication Publication No. 2005-509327.

It is supposed that a mobile communication terminal device is makingwireless communication with a first base station, and is moving in adirection from the first base station towards a second base stationdisposed adjacent to the first base station. If the mobile communicationterminal device detects reduction in a strength of an electric field forreceiving signals from the first base station, increase in power fortransmitting signals, or increase in a signal-interference ratio (SIR)in the second base station, the mobile communication terminal devicetreats them as triggers for starting carrying out handover to the secondbase station from the first base station.

DISCLOSURE OF THE INVENTION

Recently, there has been suggested a mobile communication terminaldevice including a plurality of wireless interfaces different from oneanother with respect to a communication system.

For instance, if a mobile communication terminal device including a WLANwireless interface and a W-CDMA wireless interface, during makingwireless communication in accordance with WLAN, could not maintainmaking the communication, the mobile communication terminal deviceswitches a communication system from WLAN to W-CDMA to thereby restartmaking wireless communication.

However, since it takes time to restart the communication by switching acommunication system, serviceability to a user is much deteriorated inreal-time service such as voice communication or visual telephonecommunication.

In comparison with the conventional cellular system, a bandwidth is notensured for each user in WLAN system in which packet communication isbasically carried out. Accordingly, even if wireless quality were high,communication might be much delayed, voices might be interrupted, orvoices might be delayed, resulting in much deterioration inserviceability to users.

Accordingly, if only a strength of an electric field for receivingwireless signals is used as a factor in accordance with which whetherhandover should be carried out is determined, only signal-receivingquality would be considered. This means that a strength of an electricfield for receiving wireless signals is not sufficient for measuringcommunication quality in wireless communication.

For instance, if a strength of an electric field for receiving wirelesssignals were high, but the communication in the area were very crowded,it would be substantially impossible to provide sufficient real-timeservice (voice communication and visual communication) to users.

Furthermore, even if a strength of an electric field for receivingwireless signals were sufficiently high, wireless signals sometimescould not reach an access point. Thus, if only a strength of an electricfield for receiving wireless signals is used as a timing factor inaccordance with which whether handover should be carried out isdetermined, communication might be instantaneously interrupted.

In addition, even if wireless link between an access point and a mobilecommunication terminal device were sufficiently qualified, a networkbetween the access point and a mobile communication terminal device withwhich the first mentioned mobile communication terminal device is goingto make communication might be crowded, resulting in that a user cannotreceive sufficient real-time service.

Furthermore, power for transmitting wireless signals is weak in awireless communication system in which an administrator is not necessaryto have a license to make wireless communication, such as WLAN, an areain which wireless signals can reach is not so wide. Thus, it isdifficult to maintain communication quality high around an area in whichwireless signals can reach.

Moreover, since internal interferences occur in a mobile communicationterminal device including a plurality of wireless interfaces differentfrom one another with respect to a communication system, it sometimestakes much time to retrieve a wireless station to which handover isdirected.

SUMMARY OF THE INVENTION

In view of the above-mentioned problems in the conventional mobilewireless communication system, it is an object of the present inventionto provide a mobile wireless communication system, a method of carryingout handover in the system, a wireless station used in the system, amobile communication terminal device used in the system, a program forcausing the wireless station to carry out the method, and a program forcausing the mobile communication terminal device to carry out themethod, all of which are capable of carrying out handover withoutinterruption or with no interruption in communication.

Solution to the Problems

In order to achieve the above-mentioned object, the present inventionprovides a mobile wireless communication system including a network, aretrieval server connected in wireless communication to the network, aplurality of wireless stations connected in wireless communication tothe network, and a mobile communication terminal device makingcommunication, keeping a first wireless link comprising a pair of uplinkand downlink with one of the wireless stations, wherein when a strengthof an electric field for receiving wireless in the downlink is equal toor smaller than a predetermined strength, the mobile communicationterminal device transmits a retrieval request to the retrieval serverthrough a wireless station through which the mobile communicationterminal device is making wireless communication, to cause the retrievalserver to start selecting a new wireless station, changes at least oneof profiles (UTP) for transmitting wireless in the uplink, and notifiesthe wireless station of the changed profile(s), the wireless stationchanges a profile or profiles (URP) for receiving wireless in uplink,corresponding to the changed profile(s) (UTP) for transmitting wirelessin the uplink, received from the mobile wireless terminal device,changes at least one of profiles (DTP) for transmitting wireless in thedownlink, and notifies the mobile wireless terminal device of thechanged profile(s) (DTP) for transmitting wireless in the downlink, themobile communication terminal device, until the mobile communicationterminal device establishes a second wireless link with the new wirelessstation notified from the retrieval server, changes a profile orprofiles (DRP) for receiving wireless in downlink, corresponding to thechanged profile(s) for transmitting wireless in the downlink, receivedfrom the wireless station, to maintain the first wireless link with thewireless station.

The wireless station may be comprised of an access point having a WLAN(Wireless Local Area Network) function, for instance.

The mobile communication terminal device changes at least one ofprofiles (UTP) for transmitting wireless in the uplink, based on astrength of an electric field for receiving wireless, an electric powerfor transmitting wireless, and an error rate, for instance.

At least one of profiles (UTP) for transmitting wireless in the uplinkis modulation, for instance.

At least one of profiles (UTP) for transmitting wireless in the uplinkis a coding rate, for instance.

In the case that the first wireless link is established in accordancewith OFDMA (Orthogonal Frequency Division Multiple Access), at least oneof profiles (UTP) for transmitting wireless in the uplink is a number ofsub-channels in the OFDMA, for instance.

It is preferable that the wireless station, on receipt of notificationthat a profile or profiles for transmitting wireless in the uplinkhas(have) been changed, from the mobile communication terminal device,changes at least one of profiles (DTP) for transmitting wireless in thedownlink, based on a strength of an electric field for receivingwireless, an electric power for transmitting wireless, and an errorrate.

At least one of profiles (DTP) for transmitting wireless in the downlinkmay be modulation, for instance.

At least one of profiles (DTP) for transmitting wireless in the downlinkmay be a coding rate, for instance.

At least one of profiles (DTP) for transmitting wireless in the downlinkmay be a number of sub-channels in the OFDMA, for instance.

The mobile communication terminal device may be designed to transmit theretrieval request to the retrieval server through the wireless stationwhen a number of packet collisions exceeds a predetermined threshold.

The mobile communication terminal device may be designed to transmit theretrieval request to the retrieval server through the wireless stationwhen propagation delay of packets exceeds a predetermined threshold.

The mobile communication terminal device may be designed to include aplurality of wireless interfaces different from each other with respectto a communication system, in which case, the mobile communicationterminal device may be designed to simultaneously establish a pluralityof wireless links with a plurality of wireless stations including thewireless station through which the mobile communication terminal deviceis making wireless communication, through the plurality of wirelessinterfaces, detect internal interference among the plurality of wirelessinterfaces, and cancel the internal interference by changing profilesfor operating one of the plurality of wireless interfaces.

The mobile communication terminal device may be comprised of a mobilephone, for instance.

The present invention further provides a method of carrying out handoverin a mobile wireless communication system including: a network, aretrieval server connected in wireless communication to the network, aplurality of wireless stations connected in wireless communication tothe network, and a mobile communication terminal device makingcommunication, keeping a first wireless link comprising a pair of uplinkand downlink with one of the wireless stations, the method including afirst step in which, when a strength of an electric field for receivingwireless in the downlink is equal to or smaller than a predeterminedstrength, the mobile communication terminal device transmits a retrievalrequest to the retrieval server through a wireless station through whichthe mobile communication terminal device is making wirelesscommunication, to cause the retrieval server to start selecting a newwireless station, changes at least one of profiles (UTP) fortransmitting wireless in the uplink, and notifies the wireless stationof the changed profile(s), a second step in which the wireless stationchanges a profile or profiles (URP) for receiving wireless in uplink,corresponding to the changed profile(s) (UTP) for transmitting wirelessin the uplink, received from the mobile wireless terminal device,changes at least one of profiles (DTP) for transmitting wireless in thedownlink, and notifies the mobile wireless terminal device of thechanged profile(s) (DTP) for transmitting wireless in the downlink, athird step in which the mobile communication terminal device, until themobile communication terminal device establishes a second wireless linkwith the new wireless station notified from the retrieval server,changes a profile or profiles (DRP) for receiving wireless in downlink,corresponding to the changed profile(s) (DTP) for transmitting wirelessin the downlink, received from the wireless station, to maintain thefirst wireless link with the wireless station, and a fourth step inwhich the mobile communication terminal device establishes a secondwireless link with the new wireless station notified from the retrievalserver.

The wireless station is comprised of an access point having a WLAN(Wireless Local Area Network) function, for instance.

It is preferable that at least one of profiles (UTP) for transmittingwireless in the uplink is changed in the first step, based on a strengthof an electric field for receiving wireless, an electric power fortransmitting wireless, and an error rate.

For instance, modulation may be selected as at least one of profiles(UTP) for transmitting wireless in the uplink.

For instance, a coding rate may be selected as at least one of profiles(UTP) for transmitting wireless in the uplink.

In the case that the first wireless link is established in accordancewith OFDMA (Orthogonal Frequency Division Multiple Access), at least oneof profiles (UTP) for transmitting wireless in the uplink may be anumber of sub-channels in the OFDMA, for instance.

It is preferable that the wireless station, on receipt of notificationthat a profile or profiles for transmitting wireless in the uplinkhas(have) been changed, from the mobile communication terminal device,changes in the second step at least one of profiles (DTP) fortransmitting wireless in the downlink, based on a strength of anelectric field for receiving wireless, an electric power fortransmitting wireless, and an error rate.

For instance, modulation may be selected as at least one of profiles(DTP) for transmitting wireless in the downlink.

For instance, a coding rate may be selected as at least one of profiles(DTP) for transmitting wireless in the downlink.

For instance, a number of sub-channels in the OFDMA may be selected asat least one of profiles (DTP) for transmitting wireless in thedownlink.

It is preferable that the mobile communication terminal device transmitsthe retrieval request to the retrieval server through the wirelessstation in the first step when a number of packet collisions exceeds apredetermined threshold.

It is preferable that the mobile communication terminal device transmitsthe retrieval request to the retrieval server through the wirelessstation in the first step when propagation delay of packets exceeds apredetermined threshold.

The mobile communication terminal device may be designed to include aplurality of wireless interfaces different from each other with respectto a communication system, in which case, it is preferable that themethod further includes a step in which the mobile communicationterminal device simultaneously establishes a plurality of wireless linkswith a plurality of wireless stations including the wireless stationthrough which the mobile communication terminal device is makingwireless communication, through the plurality of wireless interfaces,detects internal interference among the plurality of wirelessinterfaces, and cancels the internal interference by changing profilesfor operating one of the plurality of wireless interfaces.

The present invention further provides a wireless station to be used ina mobile wireless communication system including: a network, a retrievalserver connected in wireless communication to the network, a pluralityof wireless stations connected in wireless communication to the network,and a mobile communication terminal device making communication, keepinga first wireless link comprising a pair of uplink and downlink with oneof the wireless stations, wherein, in the case that, when a strength ofan electric field for receiving wireless in the downlink is equal to orsmaller than a predetermined strength, the mobile communication terminaldevice transmits a retrieval request to the retrieval server through awireless station through which the mobile communication terminal deviceis making wireless communication, to cause the retrieval server to startselecting a new wireless station, changes at least one of profiles (UTP)for transmitting wireless in the uplink, and notifies the wirelessstation of the changed profile(s), the wireless station changes aprofile or profiles (URP) for receiving wireless in uplink,corresponding to the changed profile(s) (UTP) for transmitting wirelessin the uplink, received from the mobile wireless terminal device,changes at least one of profiles (DTP) for transmitting wireless in thedownlink, and notifies the mobile wireless terminal device of thechanged profile(s) (DTP) for transmitting wireless in the downlink.

The wireless station is comprised of an access point having a WLAN(Wireless Local Area Network) function, for instance.

It is preferable that the mobile communication terminal device, onreceipt of notification that a profile or profiles for transmittingwireless in the uplink has(have) been changed, from the mobilecommunication terminal device, changes at least one of profiles (UTP)for transmitting wireless in the uplink, based on a strength of anelectric field for receiving wireless, an electric power fortransmitting wireless, and an error rate.

For instance, modulation may be selected as at least one of profiles(UTP) for transmitting wireless in the uplink.

For instance, a coding rate may be selected as at least one of profiles(UTP) for transmitting wireless in the uplink.

For instance, a number of sub-channels in the OFDMA may be selected asat least one of profiles (UTP) for transmitting wireless in the uplink.

The present invention further provides a mobile communication terminaldevice in a mobile wireless communication system including: a network, aretrieval server connected in wireless communication to the network, aplurality of wireless stations connected in wireless communication tothe network, and the mobile communication terminal device, the mobilecommunication terminal device making communication, keeping a firstwireless link comprising a pair of uplink and downlink with one of thewireless stations, wherein when a strength of an electric field forreceiving wireless in the downlink is equal to or smaller than apredetermined strength, the mobile communication terminal devicetransmits a retrieval request to the retrieval server through a wirelessstation through which the mobile communication terminal device is makingwireless communication, to cause the retrieval server to start selectinga new wireless station, changes at least one of profiles (UTP) fortransmitting wireless in the uplink, and notifies the wireless stationof the changed profile(s), when the wireless station changes a profileor profiles (URP) for receiving wireless in uplink, corresponding to thechanged profile(s) (UTP) for transmitting wireless in the uplink,received from the mobile wireless terminal device, changes at least oneof profiles (DTP) for transmitting wireless in the downlink, andnotifies the mobile wireless terminal device of the changed profile(s)(DTP) for transmitting wireless in the downlink, the mobilecommunication terminal device, until the mobile communication terminaldevice establishes a second wireless link with the new wireless stationnotified from the retrieval server, changes a profile or profiles (DRP)for receiving wireless in downlink, corresponding to the changedprofile(s) for transmitting wireless in the downlink, received from thewireless station, to maintain the first wireless link with the wirelessstation.

It is preferable that the mobile communication terminal device changesat least one of profiles (UTP) for transmitting wireless in the uplink,based on a strength of an electric field for receiving wireless, anelectric power for transmitting wireless, and an error rate.

There may be selected modulation as at least one of profiles (UTP) fortransmitting wireless in the uplink.

There may be selected a coding rate as at least one of profiles (UTP)for transmitting wireless in the uplink for instance.

It is preferable that the mobile communication terminal device transmitsthe retrieval request to the retrieval server through the wirelessstation when a number of packet collisions exceeds a predeterminedthreshold.

It is preferable that the mobile communication terminal device transmitsthe retrieval request to the retrieval server through the wirelessstation when propagation delay of packets exceeds a predeterminedthreshold.

The mobile communication terminal device may be designed to include aplurality of wireless interfaces different from each other with respectto a communication system, in which case, it is preferable that themobile communication terminal device simultaneously establishes aplurality of wireless links with a plurality of wireless stationsincluding the wireless station through which the mobile communicationterminal device is making wireless communication, through the pluralityof wireless interfaces, detects internal interference among theplurality of wireless interfaces, and cancels the internal interferenceby changing profiles for operating one of the plurality of wirelessinterfaces.

The mobile communication terminal device may be comprised of a mobilephone, for instance.

The present invention further provides a program for causing a computermounted in a wireless station to carry out a method of carrying outhandover in a mobile wireless communication system including: a network,a retrieval server connected in wireless communication to the network, aplurality of wireless stations connected in wireless communication tothe network, and a mobile communication terminal device makingcommunication, keeping a first wireless link comprising a pair of uplinkand downlink with one of the wireless stations, wherein steps executedby the computer in accordance with the program includes a step in whichin the case that, when a strength of an electric field for receivingwireless in the downlink is equal to or smaller than a predeterminedstrength, the mobile communication terminal device transmits a retrievalrequest to the retrieval server through a wireless station through whichthe mobile communication terminal device is making wirelesscommunication, to cause the retrieval server to start selecting a newwireless station, changes at least one of profiles (UTP) fortransmitting wireless in the uplink, and notifies the wireless stationof the changed profile(s), the wireless station changes a profile orprofiles (URP) for receiving wireless in uplink, corresponding to thechanged profile(s) (UTP) for transmitting wireless in the uplink,received from the mobile wireless terminal device, changes at least oneof profiles (DTP) for transmitting wireless in the downlink, andnotifies the mobile wireless terminal device of the changed profile(s)(DTP) for transmitting wireless in the downlink.

The present invention further provides a program for causing a computermounted in a mobile communication terminal device to carry out a methodof carrying out handover in a mobile wireless communication systemincluding: a network, a retrieval server connected in wirelesscommunication to the network, a plurality of wireless stations connectedin wireless communication to the network, and a mobile communicationterminal device making communication, keeping a first wireless linkcomprising a pair of uplink and downlink with one of the wirelessstations, wherein steps executed by the computer in accordance with theprogram includes a first step in which in the case that, when a strengthof an electric field for receiving wireless in the downlink is equal toor smaller than a predetermined strength, the mobile communicationterminal device transmits a retrieval request to the retrieval serverthrough a wireless station through which the mobile communicationterminal device is making wireless communication, to cause the retrievalserver to start selecting a new wireless station, changes at least oneof profiles (UTP) for transmitting wireless in the uplink, and notifiesthe wireless station of the changed profile(s), a second step in whichwhen the wireless station changes a profile or profiles (URP) forreceiving wireless in uplink, corresponding to the changed profile(s)(UTP) for transmitting wireless in the uplink, received from the mobilewireless terminal device, changes at least one of profiles (DTP) fortransmitting wireless in the downlink, and notifies the mobile wirelessterminal device of the changed profile(s) (DTP) for transmittingwireless in the downlink, the mobile communication terminal devicechanges a profile or profiles (DRP) for receiving wireless in downlink,corresponding to the changed profile(s) (DTP) for transmitting wirelessin the downlink, received from the wireless station, to maintain thefirst wireless link with the wireless station, and a third step in whichthe mobile communication terminal device establishes a second wirelesslink with the new wireless station notified from the retrieval server.

The above and other objects and advantageous features of the presentinvention will be made apparent from the following description made withreference to the accompanying drawings, in which like referencecharacters designate the same or similar parts throughout the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptional view of the mobile wireless communicationsystem in accordance with the first exemplary embodiment of the presentinvention.

FIG. 2 is a block diagram illustrating a structure of the mobilecommunication terminal device used in the mobile wireless communicationsystem in accordance with the first exemplary embodiment of the presentinvention.

FIG. 3 is a block diagram showing an example of a control circuitmounted in the mobile communication terminal device used in the mobilewireless communication system in accordance with the first exemplaryembodiment of the present invention.

FIG. 4 is a block diagram illustrating a structure of the first wirelessstation used in the mobile wireless communication system in accordancewith the first exemplary embodiment of the present invention.

FIG. 5 is a flow-chart showing an operation of the control circuitmounted in the mobile communication terminal device used in the mobilewireless communication system in accordance with the first exemplaryembodiment of the present invention.

FIG. 6 is a flow-chart showing an operation of a control circuitequipped in the first wireless station used in the mobile wirelesscommunication system in accordance with the first exemplary embodimentof the present invention.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 1 is a conceptional view of the mobile wireless communicationsystem in accordance with the first exemplary embodiment of the presentinvention.

The mobile wireless communication system in accordance with the firstexemplary embodiment is comprised of a network 100, a retrieval server102 capable of making wireless communication through the network 100, aplurality of wireless stations each capable of making wirelesscommunication through the network 100 (only a first wireless station 103and a second wireless station 104 are illustrated in FIG. 1), and amobile communication terminal device 105 making wireless communication,keeping a first wireless link comprising a pair of uplink and downlinkwith one of the wireless stations.

The network 100 is comprised of Internet, for instance.

The retrieval server 102 includes a database indicating a location ofeach of the wireless stations. On receipt of a retrieval request fromthe mobile communication terminal device 105, the retrieval server 102retrieves the database to identify a wireless station located in thevicinity of the mobile communication terminal device 105 in accordancewith both a location of the mobile communication terminal device 105 anda direction in which the mobile communication terminal device 105 moves.

Each of the first wireless station 103 and the second wireless station104 is comprised of a WLAN access point or a mobile communicationnetwork base station. In the first exemplary embodiment, the firstwireless station 103 is comprised of a WLAN access point, and the secondwireless station 104 is comprised of a WLAN access point or a mobilecommunication network base station.

The mobile communication terminal device 105 is comprised of a mobilephone, for instance.

FIG. 1 illustrates that the mobile communication terminal device 105establishes wireless link with the first wireless station 103, is makingwireless communication with a communication terminal device 106 throughthe network 100, and starts moving in a direction A during thecommunication, approaching the second wireless station 104.

FIG. 2 is a block diagram of the mobile communication terminal device105 in the first exemplary embodiment.

As illustrated in FIG. 2, the mobile communication terminal device 105includes an OFDMA (Orthogonal Frequency Division Multiple Access)wireless interface 201, a W-CDMA (Wideband Code Division MultipleAccess) wireless interface 202, a decoder 203, a circuit 204 fordisassembling packets, a packet 205 for assembling packets, an encoder206, a measuring circuit 207, a codec 208, a control circuit 209, acircuit 210 for measuring an error rate, a circuit 211 for detectingpacket collision, a circuit 212 for measuring reciprocating propagationdelay, and an antenna 213.

The OFDMA wireless interface 201 establishes a plurality of sub-channelswith a wireless station comprised of a WLAN access point.

The W-CDMA wireless interface 202 establishes a spread spectrum channelwith a wireless station comprised of a mobile communication network basestation.

The mobile communication terminal device 105 and the communicationterminal device 106 transmit signals to and receive signals from eachother through the codec 208 and the W-CDMA wireless interface 202.

Signals having been received at the OFDMA wireless interface 201 throughthe antenna 213 are decoded in the decode 203, and then, converted intooriginal digital signals in the packet⁻disassembling circuit 204.

User data to be transmitted are assembled into packets in thepacket-assembling circuit 205, encoded in the encoder 206, and then,transmitted through the OFDMA wireless interface 201 and the antenna213.

FIG. 3 is a block diagram of an exemplary structure of the controlcircuit 209.

The control circuit 209 is comprised of a central processing unit (CPU)2091, a first memory 2092, a second memory 2093, an input interface 2094through which a command and/or data is input into the central processingunit 2091, an output interface 2095 through which a result of stepshaving been executed by the central processing unit 2091 is output, andbuses 2096 through which the central processing unit 2091 iselectrically connected with the other parts.

Each of the first and second memories 2092 and 2093 is comprised of asemiconductor memory such as a read only memory (ROM), a random accessmemory (RAM) or an IC memory card, or a storage device such as aflexible disc, a hard disc or an optic magnetic disc. In the presentexemplary embodiment, the first memory 2092 comprises a ROM, and thesecond memory 2093 comprises a RAM.

The first memory 2092 stores therein fixed data such as a program to beexecuted by the central processing unit 2091. The second memory 2093stores therein various data and parameters, and provides an area for thecentral processing unit 2091 to operate therein. That is, the secondmemory 2093 stores data therein temporarily necessary for the centralprocessing unit 2091 to execute the program.

The central processing unit 2091 reads the program out of the firstmemory 2092, and executes the program. In other words, the centralprocessing unit 2091 operates in accordance with the program stored inthe first memory 2092.

The measuring circuit 207 is comprised of a circuit 221 for measuring astrength of an electric field for receiving signals, and a circuit 222for measuring a power for transmitting signals. The measuring circuit207 is connected to the OFDMA wireless interface 201 and the W-CDMAwireless interface 202. The circuit 221 measures a strength of anelectric field for receiving signals, and transmits a signal indicativeof the measured strength, to the control circuit 209. The circuit 222measures a power for transmitting signals in the mobile communicationterminal device 105, and transmits a signal indicative of the measuredpower to the control circuit 209.

The error-rate measuring circuit 210 is connected to an output of thedecoder 203. The error-rate measuring circuit 210 measures an error ratein signals having been received in the OFDMA wireless interface 201, andtransmits the measures error rate to the control circuit 209.

The control circuit 209 judges quality of a wireless link establishedbetween the mobile communication terminal device 105 and the firstwireless station 103, based on a strength of an electric field forreceiving signals, received from the circuit 221, a power fortransmitting signals, received from the circuit 222, and an error ratereceived from the error-rate measuring circuit 210.

For instance, if signals transmitted from the first wireless station(access point) 103 can readily reach the mobile communication terminaldevice 105, and signals transmitted from the mobile communicationterminal device 105 can readily reach the first wireless station (accesspoint) 103, the control circuit 209 judges that a wireless linkestablished between the mobile communication terminal device 105 and thefirst wireless station 103 has high quality.

The control circuit 209 varies profiles in the mobile communicationterminal device 105 for transmitting signals, in accordance with thejudgment results, as mentioned later.

When a strength of an electric field for receiving signals is equal toor smaller than a predetermined strength, the control circuit 209transmits a retrieval request packet to the retrieval server 102 throughthe packet-assembling circuit 205, the encoder 206, the OFDMA wirelessinterface 201, and the antenna 213.

The control circuit 209 simultaneously determines modulation, a numberof sub-channels, and a coding rate in uplink in accordance with theabove-mentioned three measurements for reestablishing the OFDMA wirelessinterface 201 and the encoder 206, and transmits the thus determinedoperational profiles in uplink to the first wireless station 103 ascontrol packets (a request for changing profiles) through thepacket-assembling circuit 205.

On receipt of the control packets from the mobile communication terminaldevice 105, the first wireless station 103 determines modulation, anumber of sub-channels, and a coding rate in downlink in accordance withthe above-mentioned three measurements having been measured by the firstwireless station 103, and changes current modulation, a current numberof sub-channels, and a current coding rate into the thus determinedmodulation, number and rate, and further, notifies the mobilecommunication terminal device 105 of the thus determined operationalprofiles in downlink.

Signals indicative of the operational profiles in downlink transmittedto the mobile communication terminal device 105 from the first wirelessstation 103 are converted in the packet-disassembling circuit 204 intocontrol data used for controlling receiving signals, and then,transmitted to the control circuit 209. The control circuit 209 changesdemodulation in the OFDMA wireless interface 201, and a number ofsub-channels in accordance with the received control data.

The circuit 211 detects collision of packets. The packet-collisiondetecting circuit 211 is connected to both the packet-assembling circuit205 and the packet-disassembling circuit 204. The packet-collisiondetecting circuit 211 counts a number by which packets having beentransmitted from the mobile communication terminal device 105 collidewith other packets on a transmission path, to thereby judgecommunication quality except the above-mentioned wireless link.

When communication traffic increases in a common area, the mobilecommunication terminal device 105 attempts to transmit data such thatthe data does not interfere with data transmitted from other mobilecommunication terminal devices. However, the greater a number ofcollision is, the lower estimate to communication quality in the areais.

The circuit 212 is connected to both the packet-assembling circuit 205and the packet-disassembling circuit 204, and measures a reciprocatingpropagation time in which packets transmitted from the mobilecommunication terminal device 105 are received by the communicationterminal device 106, and reply packets transmitted from thecommunication terminal device 106 reach the mobile communicationterminal device 105.

The measured reciprocating propagation time is transmitted to thecontrol circuit 209. The control circuit 209 judges quality ofcommunication made between the mobile communication terminal device 105and the communication terminal device 106, in accordance with how muchdegree the measured reciprocating propagation time delays in comparisonwith standard reciprocating propagation time.

Specifically, since a lot of routers exist between the first wirelessstation 103 and the communication terminal device 106, a period of timenecessary for signals to arrive at the communication terminal device 106from the mobile communication terminal device 105 varies in dependenceon communication traffic passing through the routers. The controlcircuit 109 judges that the shorter the propagation delay time is, thehigher communication quality on network between the mobile communicationterminal device 105 and the communication terminal device 106 is, andvice versa.

The control circuit 209 further compares a number of packet collisionsindicated in the signal transmitted from the circuit 211 to apredetermined number. If a number of packet collisions is equal to orgreater than the predetermined number, the control circuit 209 transmitsa retrieval request to the retrieval server 102.

The control circuit 209 further compares the reciprocating propagationtime indicated in the signal transmitted from the circuit 212 to apredetermined time. If the reciprocating propagation time is equal to orgreater than the predetermined time, the control circuit 209 transmits aretrieval request to the retrieval server 102.

The measuring circuit 207 monitors whether internal interference, whichoccurs between the OFDMA wireless interface 201 and the W-CDMA wirelessinterface 202 when both of them operate, occurs. If the measuringcircuit 207 detects the internal interference, the measuring circuit 207transmits a signal 207 a indicative of the detection of the internalinterference to the control circuit 209.

On receipt of the signal 207 a indicative of the detection of theinternal interference, the control circuit 209 varies wireless profilesof the W-CDMA wireless interface 202 to thereby stop the internalinterference. It is possible to stop the internal interference byvarying wireless profiles of the OFDMA wireless interface 201, ifhandover is not being carried out.

FIG. 4 is a block diagram showing a structure of the first wirelessstation 103.

As illustrated in FIG. 4, the first wireless station 103 is comprised ofan OFDMA wireless interface 301, a decoder 302, a network interface 303,an encoder 304, a circuit 305 for measuring an error rate, a measuringcircuit 306, a control circuit 307, and an antenna 308.

Signals having been transmitted from the mobile communication terminaldevice 105 are received by the OFDMA wireless interface 301, input intothe decoder 302, and decoded in the decoder 302.

The decoded signals are transmitted to the communication network 100through the network interface 303, and then, transmitted to thecommunication terminal device 106 through the communication network 100.

Signals transmitted from the communication terminal device 106 are inputinto the network interface 303 through the communication network 100,and then, encoded in the encoder 304. Then, the signals are transmittedto the mobile communication terminal device 105 through the OFDMAwireless interface 301.

The error-rate measuring circuit 305 is connected to an output of thedecoder 302. The error-rate measuring circuit 305 measures an error rateof signals having been transmitted from the mobile communicationterminal device 105, and notifies the control circuit 307 of themeasurement.

The measuring circuit 306 is comprised of a circuit 311 for measuring astrength of an electric field for receiving signals, and a circuit 312for measuring a power for transmitting signals. The measuring circuit306 is connected to the OFDMA wireless interface 301. The circuit 311measures a strength of an electric field for receiving signals, andtransmits a signal indicative of the measured strength, to the controlcircuit 307. The circuit 312 measures a power for transmitting signalsin the first wireless station 103, and transmits a signal indicative ofthe measured power to the control circuit 307.

The control circuit 307 has the same structure as that of the controlcircuit 209 of the mobile communication terminal device 105 illustratedin FIG. 3. Specifically, a central processing unit in the controlcircuit 307 reads a program out of a first memory, and executes theprogram. That is, the central processing unit in the control circuit 307operates in accordance with the program stored in the first memory.

On receipt of the retrieval request from the mobile communicationterminal device 105, the control circuit 307 transmits a retrievalrequest packet to the retrieval server 102 through the network interface303, and receives a reply thereof as data indicative of an access point(AP).

On receipt of a request to change a profile or profiles from the mobilecommunication terminal device 105, the control circuit 307 determinesmodulation, a number of sub-channels, and a coding rate in accordancewith a strength of an electric field for receiving signals, a power fortransmitting signals, and an error rate in received signals in the firstwireless station 103, applies the determined modulation, number and rateto associated devices thereof, and notifies the mobile communicationterminal device 105 of the determined modulation, number and rate.

FIG. 5 is a flow-chart showing an operation of the control circuit 209of the mobile communication terminal device 105 in the mobile wirelesscommunication system in accordance with the present exemplaryembodiment.

The operation of the control circuit 209 of the mobile communicationterminal device 105 in the present exemplary embodiment is explainedhereinbelow with reference to FIG. 5.

It is supposed that the mobile communication terminal device 105presently uses the OFDMA wireless interface 201, and has wireless linkwith the first wireless station 103 comprised of a WLAN access point.

First, the control circuit 209 judges whether a strength of an electricfield in the signals having been transmitted from the first wirelessstation 103 is equal to or smaller than a predetermined strength (step401).

If a strength of an electric field in the signals having beentransmitted from the first wireless station 103 is equal to or smallerthan a predetermined strength (YES in step 401), the control circuit 209transmits a retrieval request packet to the retrieval server 102 (step402).

Then, the control circuit 209 receives both a strength of an electricfield for receiving signals in downlink and a power for transmittingsignals in uplink from the measuring circuit 207, and further receivesan error rate in downlink from the error-rate measuring circuit 210 tothereby determine profiles (UTP) (modulation, a number of sub-channelsfor transmitting signals, and a coding rate in uplink) for transmittingsignals in uplink, which indicate a plurality of operational profiles inuplink in the mobile communication terminal device 105 (step 403).

Then, the control circuit 209, as a result of the uplinksignal-transmission profiles (UTP) being changed, transmits how theuplink signal-transmission profiles (UTP) was changed by the mobilecommunication terminal device 105 to the first wireless station 103 as amessage for requesting changing profiles (URP) for receiving signals inuplink in the first wireless station 103 (step 404).

Then, the control circuit 209 receives a message for requesting changingdownlink signal-receipt profiles (DRP) from the first wireless station103 (step 405).

Then, the control circuit 209 changes modulation, demodulation, a numberof sub-channels for transmitting signals, a number of sub-channels forreceiving signals, and a coding rate in accordance with both the uplinksignal-transmission profiles (UTP) having been determined before, andthe downlink signal-receipt profiles (DRP) having been received from thefirst wireless station 103 (step 406).

It is possible for signals to reach as far as possible by changing themodulation.

Specifically, by changing 64 QAM into modulation having a low modulationrate, such as 16 QAM or 4 PSK, a signal can reach remoter in modulationhaving a low modulation rate than in modulation having a high modulationrate, even if the signal is transmitted at the same signal-transmissionpower.

Furthermore, it is possible to enhance ability of correcting an errorfor readily reproducing data by changing a coding rate such thatredundant data increases.

In addition, it is possible to increase a maximum distance by which asignal can reach, by reducing a number of sub-channels to thereby raisean energy density per a sub-channel.

Then, the control circuit 209 receives a list of candidates of wirelessstations from the retrieval server 102, and selects the most optimalwireless station among them (step 407).

Thereafter, the control circuit 209 judges whether the selected wirelessstation is a base station for a mobile communication network (step 408).Specifically, the control circuit 209 judges whether the selectedwireless station is a base station for a mobile communication network ora wireless access point.

If the selected wireless station is a wireless access point (NO in step408), the control circuit 209 establishes wireless link with the newlyselected wireless station through the OFDMA wireless interface 201 whichthe mobile communication terminal device 105 presently uses, andnotifies the newly selected wireless station of an address of thecommunication terminal device 106 (step 412).

Then, the control circuit 209 releases the previously used wireless link(step 413).

Thereafter, the control circuit 209 repeatedly carries out step 401 andthe subsequent steps.

If the selected wireless station is a base station for a mobilecommunication network (YES in step 408), the control circuit 209establishes wireless link with the newly selected wireless stationthrough the W-CDMA wireless interface 202, and notifies the newlyselected wireless station of an address of the communication terminaldevice 106 (step 409).

Then, the control circuit 209 judges whether there exists internalinterference between the OFDMA wireless interface 201 and the W-CDMAwireless interface 202, in accordance with the signal 207 a receivedfrom the measuring circuit 207 (step 410).

If there exists no internal interference (NO in step 410), the controlcircuit 209 releases the previously used wireless link (step 413).

If there exists internal interference (YES in step 410), the controlcircuit 209 prevents internal interference by changing wireless profilesof the W-CDMA wireless interface 202 (step 411).

Then, the control circuit 209 releases the previously used wireless link(step 413).

Thereafter, the control circuit 209 repeatedly carries out step 401 andthe subsequent steps.

If a strength of an electric field in the signals having beentransmitted from the first wireless station 103 is greater than thepredetermined strength (NO in step 401), the control circuit 209 judgeswhether a number of packet collisions indicated in a signal transmittedfrom the packet-collision detecting circuit 211 is greater than apredetermined number (step 421).

If a number of packet collisions is greater than the predeterminednumber (YES in step 421), the control circuit 209 transmits a retrievalrequest to the retrieval server 102 (step 423).

Thereafter, the control circuit 209 carries out step 407 and thesubsequent steps to thereby newly select a wireless station, andestablishes wireless link with the newly selected wireless station(steps 407-413).

If a number of packet collisions is equal to or smaller than thepredetermined number (NO in step 421), the control circuit 209 judgeswhether t

If the reciprocating propagation delay of packets is greater than thepredetermined delay (YES in step 422), the control circuit 209 transmitsa retrieval request to the retrieval server 102 (step 423).

If the reciprocating propagation delay of packets is equal to or smallerthan the predetermined delay (NO in step 422), the control circuit 209carries out again step 410 and the subsequent steps.

FIG. 6 is a flow-chart showing an operation of the control circuit 307equipped in the first wireless station 103.

The operation of the control circuit 307 equipped in the first wirelessstation 103 is explained hereinbelow with reference to FIG. 6.

The control circuit 307 equipped in the first wireless station 103monitors whether the message (step 404 in FIG. 5) requesting changing aprofile (URP) for receiving signals in uplink is received from themobile communication terminal device 105 (step 501).

If the message for requesting changing a profile (URP) for receivingsignals in uplink is received from the mobile communication terminaldevice 105 (YES in step 501), the control circuit 307 receives both astrength of an electric field for receiving signals in uplink and apower for transmitting signals in downlink from the circuits 311 and 312of the measuring circuit 306, respectively, and further receives anerror rate in uplink from the error-rate measuring circuit 305. Then,the control circuit 307 determines profiles (DTP) (modulation, a numberof sub-channels for transmitting signals, and a coding rate) fortransmitting signals in downlink in accordance with the above-mentionedstrength, power and error rate (step 502).

Then, the control circuit 307 transmits the profiles (DTP) fortransmitting signals in downlink to the mobile communication terminaldevice 105 as a request for changing profiles (DRP) for receivingsignals in downlink (step 503).

Then, the control circuit 307 changes modulation, demodulation, a numberof sub-channels for transmitting signals, a number of sub-channels forreceiving signals, and a coding rate in uplink in accordance with boththe profiles (URP) for receiving signals in uplink received from themobile communication terminal device 105, and the profiles (DTP) fortransmitting signals in downlink (step 504).

Thereafter, the control circuit 307 repeatedly carries out step 501 andthe subsequent steps.

If the message for requesting changing a profile (URP) for receivingsignals in uplink is not received from the mobile communication terminaldevice 105 (NO in step 501), the control circuit 307 judges whether theretrieval request is received from the mobile communication terminaldevice 105 (step 511).

If the retrieval request is received from the mobile communicationterminal device 105 (YES in step 511), the control circuit 307 transmitsthe received retrieval request to the retrieval server 102 (step 512).

Thereafter, the control circuit 307 repeatedly carries out step 501 andthe subsequent steps.

Supposing that a certain wireless station has received a list ofwireless station candidates from the retrieval server 102, the wirelessstation is the second wireless station 104 which is comprised of awireless access point or a base station for a mobile wireless networkand to which handover is directed. This means that the first wirelessstation 103 does not receive a retrieval request from the mobilecommunication terminal device 105 (NO in step 511).

Thus, the later-mentioned steps 521 to 524 (surrounded with a brokenline) are carried out by the second wireless station 104.

The second wireless station 104 judges whether a list of wirelessstation candidates is received from the retrieval server 102 (step 521).

If a list of wireless station candidates is received from the retrievalserver 102 (YES in step 521), the second wireless station 104establishes wireless link with the mobile communication terminal device105, and transmits the list to the mobile communication terminal device105.

The second wireless station 104 receives an address of the communicationterminal device 106 from the mobile communication terminal device 105(step 523).

Then, the second wireless station 104 establishes wireless link with thecommunication terminal device 106 through the network 100 in accordancewith the received address (step 524).

Thereafter, the control circuit 307 repeatedly carries out step 501 andthe subsequent steps.

As explained above, the mobile communication terminal device 105 in themobile wireless communication system in accordance with the presentexemplary embodiment, if a strength of an electric field therein forreceiving signals is equal to or smaller than a predetermined strength,changes profiles for transmitting signals in accordance with a pluralityof operational parameters in order to maintain wireless link with thefirst wireless station 103 as long as possible, and notifies the firstwireless station 103 of the changed profiles.

Before changing the profiles, the mobile communication terminal device105 transmits a retrieval request to the retrieval server 102 throughthe first wireless station 103 to request the retrieval server 102 tofind another wireless station.

The retrieval server 102 retrieves a database to select a wirelessstation as the second wireless station 104 in accordance with a currentlocation of the mobile communication terminal device 105, and notifiesthe mobile communication terminal device 105 of an identification numberof the selected wireless station through the first wireless station 103.

On receipt of the notification, the mobile communication terminal device105 starts carrying out handover, establishes wireless link with thesecond wireless station 104, and notifies the second wireless station104 of an address of the communication terminal device 106.

Receiving the notification, the second wireless station 104 establisheswireless link with the communication terminal device 106 through thenetwork 100. Thus, the handover is achieved to the second wirelessstation 104 from the first wireless station 103.

The mobile communication terminal device 105 in the mobile wirelesscommunication system in accordance with the present exemplary embodimentmaintains wireless link through which the mobile communication terminaldevice 105 is presently making wireless communication with the firstwireless station 103, until the mobile communication terminal device 105newly establishes wireless link with the second wireless station 104 towhich handover is directed. Thus, continuity in communication is ensuredas long as possible after a strength of an electric field for receivingsignals in downlink has fallen below a predetermined strength, resultingin stable quality in wireless link. That is, the handover is carried outwithout interruption in communication.

INDUSTRIAL APPLICABILITY

The present invention presents handover technique suitable to a systemfor combining mobile communication and IP (internet protocol) with eachother.

Furthermore, the present invention uses both an OFDMA wireless interfaceand a W-CDMA wireless interface to make it possible to carry outhandover over systems different from each other. For instance, thepresent invention can be applied to handover to be carried out betweenWLAN and W-CDMA, and further between WiMAX, Bluetooth, iBurst orwireless USB and a conventional cellular system.

The exemplary advantages obtained by the above-mentioned exemplaryembodiments are described hereinbelow.

In the mobile wireless communication system in accordance with thepresent invention, the mobile communication terminal device maintainswireless link with a wireless station through which the mobilecommunication terminal device is presently making wirelesscommunication, by changing a profile or profiles for transmitting orreceiving wireless signals, until the mobile communication terminaldevice newly establishes wireless link with a wireless station to whichhandover is directed. Thus, it is possible to ensure continuity incommunication as long as possible after a strength of an electric fieldfor receiving wireless signals in downlink has been equal to or smallerthan a predetermined threshold, and hence, keep quality of the wirelesslink stable. That is, it is possible to guarantee carrying out handoverwithout interruption.

While the present invention has been described in connection withcertain exemplary embodiments, it is to be understood that the subjectmatter encompassed by way of the present invention is not to be limitedto those specific embodiments. On the contrary, it is intended for thesubject matter of the invention to include all alternatives,modifications and equivalents as can be included within the spirit andscope of the following claims.

1. A mobile wireless communication system comprising: a network; aplurality of wireless stations connected in wireless communication tosaid network; and a mobile communication terminal device makingcommunication, keeping a first wireless link comprising a pair of uplinkand downlink with one of said wireless stations, wherein when saidmobile communication terminal device determines that communicationquality of said downlink is low, said mobile communication terminaldevice starts to establish a second wireless link with a new wirelessstation, changes at least one of profiles (UTP) for transmittingwireless signal in said uplink, and notifies a wireless station throughwhich said mobile communication terminal device is making wirelesscommunication of the changed profile(s), said wireless station changes aprofile or profiles (URP) for receiving wireless signal in uplink,corresponding to the changed profile(s) (UTP) for transmitting wirelesssignal in said uplink, received from said mobile communication terminaldevice.
 2. The mobile wireless communication system as set forth inclaim 1, wherein said wireless station changes at least one of profiles(DTP) for transmitting wireless signal in said downlink, and notifiessaid mobile communication terminal device of the changed profile(s)(DTP) for transmitting wireless signal in said downlink, said mobilecommunication terminal device changes a profile or profiles (DRP) forreceiving wireless signal in downlink, corresponding to the changedprofile(s) for transmitting wireless signal in said downlink, receivedfrom said wireless station.
 3. The mobile wireless communication systemas set forth in claim 1, wherein said mobile communication terminaldevice determines that the communication quality of said downlink is lowwhen a strength of an electric field for receiving wireless signal insaid downlink is equal to or smaller than a predetermined strength. 4.The mobile wireless communication system as set forth in claim 1,wherein said mobile communication terminal device determines that thecommunication quality of said downlink is low when a number of packetcollisions exceeds a predetermined threshold.
 5. The mobile wirelesscommunication system as set forth in claim 1, wherein said mobilecommunication terminal device determines that the communication qualityof said downlink is low when propagation delay of packets exceeds apredetermined threshold.
 6. The mobile wireless communication system asset forth in claim 1, wherein said wireless station is comprised of anaccess point having a WLAN (Wireless Local Area Network) function. 7.The mobile wireless communication system as set forth in claim 1,wherein said mobile communication terminal device changes at least oneof profiles (UTP) for transmitting wireless signal in said uplink, basedon a strength of an electric field for receiving wireless signal, anelectric power for transmitting wireless signal, and an error rate. 8.The mobile wireless communication system as set forth in claim 7,wherein at least one of profiles (UTP) for transmitting wireless signalin said uplink is modulation.
 9. The mobile wireless communicationsystem as set forth in claim 7, wherein at least one of profiles (UTP)for transmitting wireless signal in said uplink is a coding rate. 10.The mobile wireless communication system as set forth in claim 7,wherein said first wireless link is established in accordance with OFDMA(Orthogonal Frequency Division Multiple Access), and at least one ofprofiles (UTP) for transmitting wireless signal in said uplink is anumber of sub-channels in said OFDMA.
 11. The mobile wirelesscommunication system as set forth in claim 2, wherein said wirelessstation, on receipt of notification that a profile or profiles fortransmitting wireless signal in said uplink has(have) been changed, fromsaid mobile communication terminal device, changes at least one ofprofiles (DTP) for transmitting wireless signal in said downlink, basedon a strength of an electric field for receiving wireless signal, anelectric power for transmitting wireless signal, and an error rate. 12.The mobile wireless communication system as set forth in claim 11,wherein at least one of profiles (DTP) for transmitting wireless signalin said downlink is modulation.
 13. The mobile wireless communicationsystem as set forth in claim 11, wherein at least one of profiles (DTP)for transmitting wireless signal in said downlink is a coding rate. 14.The mobile wireless communication system as set forth in claim 11,wherein said first wireless link is established in accordance with OFDMA(Orthogonal Frequency Division Multiple Access), and at least one ofprofiles (DTP) for transmitting wireless signal in said downlink is anumber of sub-channels in said OFDMA.
 15. The mobile wirelesscommunication system as set forth in claim wherein said mobilecommunication terminal device includes a plurality of wirelessinterfaces different from each other with respect to a communicationsystem, said mobile communication terminal device simultaneouslyestablishes a plurality of wireless links with the plurality of wirelessstations including said wireless station through which said mobilecommunication terminal device is making wireless communication, throughsaid plurality of wireless interfaces, detects internal interferenceamong said plurality of wireless interfaces, and cancels said internalinterference by changing profiles for operating one of said plurality ofwireless interfaces.
 16. The mobile wireless communication system as setforth in claim 1, wherein said mobile communication terminal device iscomprised of a mobile phone.
 17. A method of carrying out handover in amobile wireless communication system comprising: a network; a pluralityof wireless stations connected in wireless communication to saidnetwork; and a mobile communication terminal device makingcommunication, keeping a first wireless link comprising a pair of uplinkand downlink with one of said wireless stations, said method comprising:a first step of, by said mobile communication terminal device, starting,when it is determined that communication quality of said downlink islow, to establish a second wireless link with a new wireless station,changing at least one of profiles (UTP) for transmitting wireless signalin said uplink, and notifying a wireless station through which saidmobile communication terminal device is making wireless communication ofthe changed profile(s); and a second step of, by said wireless station,changing a profile or profiles (URP) for receiving wireless signal inuplink, corresponding to the changed profile(s) (UTP) for transmittingwireless signal, in said uplink, received from said mobile communicationterminal device.
 18. The method as set forth in claim 17, furthercomprising: a third step of, by said wireless station, changing at leastone of profiles (DTP) for transmitting wireless signal in said downlink,and notifying said mobile communication terminal device of the changedprofile(s) (DTP) for transmitting wireless signal in said downlink; anda fourth step of, by said mobile communication terminal device, changinga profile or profiles (DRP) for receiving wireless signal in downlink,corresponding to the changed profile(s) (DTP) for transmitting wirelesssignal in said downlink, received from said wireless station.
 19. Themethod as set forth in claim 17, wherein in said first step, said mobilecommunication terminal device determines that the communication qualityof said downlink is low when a strength of an electric field forreceiving wireless signal in said downlink is equal to or smaller than apredetermined strength.
 20. The method as set forth in claim 17, whereinin said first step, said mobile communication terminal device determinesthat the communication quality of said downlink is low when a number ofpacket collisions exceeds a predetermined threshold.
 21. The method asset forth in claim 17, wherein in said first step, said mobilecommunication terminal device determines that the communication qualityof said downlink is low when propagation delay of packets exceeds apredetermined threshold.
 22. The method as set forth in claim 17,wherein said wireless station is comprised of an access point having aWLAN (Wireless Local Area Network) function.
 23. The method as set forthin claim 17, wherein at least one of profiles (UTP) for transmittingwireless signal in said uplink is changed in said first step, based on astrength of an electric field for receiving wireless signal, an electricpower for transmitting wireless signal, and an error rate.
 24. Themethod as set forth in claim 23, wherein at least one of profiles (UTP)for transmitting wireless signal in said uplink is modulation.
 25. Themethod as set forth in claim 23, wherein at least one of profiles (UTP)for transmitting wireless signal in said uplink is a coding rate. 26.The method as set forth in claim 23, wherein said first wireless link isestablished in accordance with OFDMA (Orthogonal Frequency DivisionMultiple Access), and at least one of profiles (UTP) for transmittingwireless signal in said uplink is a number of sub-channels in saidOFDMA.
 27. The method as set forth in claim 18, wherein said wirelessstation, on receipt of notification that a profile or profiles fortransmitting wireless signal in said uplink has(have) been changed, fromsaid mobile communication terminal device, changes in said third step atleast one of profiles (DTP) for transmitting wireless signal in saiddownlink, based on a strength of an electric field for receivingwireless signal, an electric power for transmitting wireless signal, andan error rate.
 28. The method as set forth in claim 27, wherein at leastone of profiles (DTP) for transmitting wireless signal in said downlinkis modulation.
 29. The method as set forth in claim 27, wherein at leastone of profiles (DTP) for transmitting wireless signal in said downlinkis a coding rate.
 30. The method as set forth in claim 27, wherein saidfirst wireless link is established in accordance with OFDMA (OrthogonalFrequency Division Multiple Access), and at least one of profiles (DTP)for transmitting wireless signal in said downlink is a number ofsub-channels in said OFDMA.
 31. The method as set forth in claim 17,wherein said mobile communication terminal device includes a pluralityof wireless interfaces different from each other with respect to acommunication system, said method further includes a step of, by saidmobile communication terminal device, simultaneously establishing aplurality of wireless links with the plurality of wireless stationsincluding said wireless station through which said mobile communicationterminal device is making wireless communication, through said pluralityof wireless interfaces, detecting internal interference among saidplurality of wireless interfaces, and canceling said internalinterference by changing profiles for operating one of said plurality ofwireless interfaces.
 32. A wireless station to be used in a mobilewireless communication system comprising: a network; a plurality ofwireless stations connected in wireless communication to said network;and a mobile communication terminal device making communication, keepinga first wireless link comprising a pair of uplink and downlink with oneof said wireless stations, the wireless station comprising: a first unitthat receives, from said mobile communication terminal device, at leastone of profiles (UTP) for said mobile communication terminal devicetransmitting wireless signal in said uplink, the at least one of theprofiles being changed by said mobile communication terminal device whensaid mobile communication terminal device determines that communicationquality of said downlink is low and starts to establish a secondwireless link with a new wireless station; and a second unit thatchanges a profile or profiles (URP) for receiving wireless signal inuplink, corresponding to the changed profile(s) (UTP) for transmittingwireless signal in said uplink, received from said mobile communicationterminal device.
 33. The wireless station as set forth in claim 32,further comprising: a third unit that changes at least one of profiles(DTP) for transmitting wireless signal in said downlink, and notifiessaid mobile communication terminal device of the changed profile(s)(DTP) for transmitting wireless signal in said downlink.
 34. Thewireless station as set forth in claim 32, wherein said wireless stationis comprised of an access point having a WLAN (Wireless Local AreaNetwork) function.
 35. The wireless station as set forth in claim 33,wherein the third unit changes, on receipt of notification that aprofile or profiles for transmitting wireless signal in said uplinkhas(have) been changed, from said mobile communication terminal device,at least one of profiles (DTP) for transmitting wireless signal in saiddownlink, based on a strength of an electric field for receivingwireless signal, an electric power for transmitting wireless signal, andan error rate.
 36. The wireless station as set forth in claim 35,wherein at least one of profiles (DTP) for transmitting wireless signalin said downlink is modulation.
 37. The wireless station as set forth inclaim 35, wherein at least one of profiles (DTP) for transmittingwireless signal in said downlink is a coding rate.
 38. The wirelessstation as set forth in claim 35, wherein said first wireless link isestablished in accordance with OFDMA (Orthogonal Frequency DivisionMultiple Access), and at least one of profiles (DTP) for transmittingwireless signal in said downlink is a number of sub-channels in saidOFDMA.
 39. A mobile communication terminal device in a mobile wirelesscommunication system comprising: a network; a plurality of wirelessstations connected in wireless communication to said network; and saidmobile communication terminal device, said mobile communication terminaldevice making communication, keeping a first wireless link comprising apair of uplink and downlink with one of said wireless stations, saidmobile communication terminal device comprising: a first unit thatstarts, when it is determined that communication quality of saiddownlink is low, to establish a second wireless link with a new wirelessstation, and changes at least one of profiles (UTP) for transmittingwireless signal in said uplink; and a second unit that notifies awireless station through which said mobile communication terminal deviceis making wireless communication of the changed profile(s).
 40. Themobile communication terminal device as set forth in claim 39, furthercomprising: a third unit that receives, when said wireless stationchanges a profile or profiles (URP) for receiving wireless signal inuplink, corresponding to the changed profile(s) (UTP) for transmittingwireless signal in said uplink, received from said mobile communicationterminal device, and changes at least one of profiles (DTP) fortransmitting wireless signal in said downlink, the changed profile(s)(DTP) for transmitting wireless signal in said downlink; and a fourthunit that changes a profile or profiles (DRP) for receiving wirelesssignal in downlink, corresponding to the changed profile(s) fortransmitting wireless signal in said downlink, received from saidwireless station.
 41. The mobile communication terminal device as setforth in claim 39, wherein the first unit determines that thecommunication quality of said downlink is low when a strength of anelectric field for receiving wireless signal in said downlink is equalto or smaller than a predetermined strength.
 42. The mobilecommunication terminal device as set forth in claim 39, wherein thefirst unit determines that the communication quality of said downlink islow when a number of packet collisions exceeds a predeterminedthreshold.
 43. The mobile communication terminal device as set forth inclaim 39, wherein the first unit determines that the communicationquality of said downlink is low when propagation delay of packetsexceeds a predetermined threshold.
 44. The mobile communication terminaldevice as set forth in claim 39, wherein the first unit changes at leastone of profiles (UTP) for transmitting wireless signal in said uplink,based on a strength of an electric field for receiving wireless signal,an electric power for transmitting wireless signal, and an error rate.45. The mobile communication terminal device as set forth in claim 44,wherein at least one of profiles (UTP) for transmitting wireless signalin said uplink is modulation.
 46. The mobile communication terminaldevice as set forth in claim 44, wherein at least one of profiles (UTP)for transmitting wireless signal in said uplink is a coding rate. 47.The mobile communication terminal device as set forth in claim 39,including: a plurality of wireless interfaces different from each otherwith respect to a communication system; and a unit that simultaneouslyestablishes a plurality of wireless links with the plurality of wirelessstations including said wireless station through which said mobilecommunication terminal device is making wireless communication, throughsaid plurality of wireless interfaces, detects internal interferenceamong said plurality of wireless interfaces, and cancels said internalinterference by changing profiles for operating one of said plurality ofwireless interfaces.
 48. The mobile communication terminal device as setforth in claim 39, wherein said mobile communication terminal device iscomprised of a mobile phone.
 49. A non-transitory computer-readablestorage medium storing therein a program for causing a computer mountedin a wireless station to carry out a method of carrying out handover ina mobile wireless communication system comprising: a network; aplurality of wireless stations connected in wireless communication tosaid network; and a mobile communication terminal device makingcommunication, keeping a first wireless link comprising a pair of uplinkand downlink with one of said wireless stations, wherein the programcauses said computer to execute: a step of receiving, from said mobilecommunication terminal device, at least one of profiles (UTP) for saidmobile communication terminal device transmitting wireless signal insaid uplink, the at least one of the profiles being changed by saidmobile communication terminal device when said mobile communicationterminal device determines that communication quality of said downlinkis low and starts to establish a second wireless link with a newwireless station; and a step of changing a profile or profiles (URP) forreceiving wireless signal in uplink, corresponding to the changedprofile(s) (UTP) for transmitting wireless signal in said uplink,received from said mobile communication terminal device.
 50. Anon-transitory computer-readable storage medium storing therein aprogram for causing a computer mounted in a mobile communicationterminal device to carry out a method of carrying out handover in amobile wireless communication system comprising: a network; a pluralityof wireless stations connected in wireless communication to saidnetwork; and a mobile communication terminal device makingcommunication, keeping a first wireless link comprising a pair of uplinkand downlink with one of said wireless stations, wherein the programcauses said computer to execute: a step of starting, when it isdetermined that communication quality of said downlink is low, toestablish a second wireless link with a new wireless station, andchanging at least one of profiles (UTP) for transmitting wireless signalin said uplink; and a step of notifying a wireless station through whichsaid mobile communication terminal device is making wirelesscommunication of the changed profile(s).